Check out OSX_Mavericks_Core_Technology_Overview.pdf via http://www.apple.com/osx/preview/advanced-technologies.html. They talked about this feature for a bit in the Keynote, but after reading the specs I'm getting the impression that this is a pretty important feature that will actually have a big impact on usage. Swapping to disks has always been an important reason for things to feel slower. That's why everything seems so fast on machines with an SSD, because even if it needs to swap, writing to the SSD is way faster than to traditional HDs. With Compressed Memory it needs to swap less frequently, swaps compressed objects, and now that the MacBook Airs (and I'm sure the MBP and the rest of the Mac line-up will follow) have PCIe SSDs with "read/write performance of nearly 800MB/s", these things are going to fly!